I have a 48 volt scooter which consists of 4 x 12v 12ah batteries. I added a further 12v 12ah battery for more speed.

The problem I have is the extra volts have stopped the electric breaking system, so now I have to rely only on the mechanical break pads.

I would like to have the electrical breaking back, etc, for when the traffic is quite bad and I have to keep stopping so I am not wearing out my mechanical breaks.

I thought of a simple indicator switch that has 48v one side and 60v the other, so the switch is basically adding on the extra 12v battery then taking it away from the 48v, but the current just was too much for the switch and it burnt out.

Can anyone recommend a durable switch I can use? or further maybe a mod I can use within the controller to get the electrical breaking back, but with keeping the 60v?

I thought of a simple indicator switch that has 48v one side and 60v the other, so the switch is basically adding on the extra 12v battery then taking it away from the 48v, but the current just was too much for the switch and it burnt out.

Very bad idea. You will end up with a badly unbalanced battery pack, and the constant power glitches won't be good for battery or controller.

If your controller is refusing to do regen due to the voltage being too high, then change the voltage sensor. It will generally be fed by a resistive divider. Find the divider and change the ratio so that what it once thought was 48V is now 60V. (Assuming the rest of the electronics can handle the higher voltage of course.)